1. Field of the Invention
The present invention relates to an ink composition suitably used for inkjet recording, an inkjet recoding method, and a planographic printing plate obtained with the ink, and a producing method of the planographic printing plate. In more detail, the invention relates to an ink composition suitable for inkjet recording, which can be cured with high sensitivity to irradiation of active radiation and has sufficient flexibility of a cured material even after the ink is cured, an inkjet recoding method, a planographic printing plate obtained with the ink, and a producing method of the planographic printing plate.
2. Description of the Related Art
As an image recording method that forms, based on an image signal, an image on a recording medium such as paper, an electrophotographic method, sublimation and fusion type thermal transfer methods and an inkjet method can be cited. In the electrophotographic method, since a process of charging and exposing to form an electrostatic latent image on a photoreceptor drum is necessary, a system therefor becomes complicated, resulting in a problem of higher production cost. As for the thermal transfer method, although a device is therefor cheap, since an ink ribbon is used, there are problems in that the running cost is high and waste is generated.
On the other hand, in the inkjet method, a cheap device can be used and the ink is discharged only on a necessary image portion to directly form an image on a recording medium. Accordingly, the ink can be used efficiently and the running cost is less expensive. Furthermore, the inkjet recording method, being lower in noise, is excellent as an image recording method.
As an ink composition that can be cured by irradiation of active radiation such as UV rays (radiation-curable ink composition) such as an inkjet recording ink composition, one that can be cured with high sensitivity and can form a high quality image is demanded. When high sensitivity is achieved, high curability due to irradiation of active radiation can be imparted. Accordingly, in addition to reduction of the power consumption and lengthening of the lifetime of an active radiation generator owing to lowering of burden, because sufficient curing can be achieved, there are various advantages in that an uncured low molecular weight material can be prevented from vaporizing and obtained image strength can be prevented from deteriorating. Furthermore, improvement in image strength owing to higher sensitivity yields a longer press life of an image portion when the ink composition is applied to form an image portion of a planographic printing plate.
As a UV-curable ink composition, for instance, an ink composition in which a plurality of monomers having different degrees of functionality are combined and used is proposed (for instance, JP-A-5-214280). However, in order to maintain the curing speed in such an ink composition, a polyfunctional monomer has to be used in a large amount, and in such a case, there is a problem with respect to the flexibility of an image after the ink is cured.
Furthermore, conventionally, when a planographic printing plate is prepared, a so-called PS plate that has a constitution in which a lipophilic photosensitive resin layer is disposed on a hydrophilic support is used, the photosensitive resin layer is imagewise exposed to increase or lower the solubility of an exposed portion to an alkali developer to form an image, and a non-image portion is dissolved and removed. However, in recent years, digital technology in which a computer is used to electronically process, store and output image information is in wide use. Accordingly, a new image output process corresponding thereto is in demand. In particular, a method that does not include processing with a developer to prepare a printing plate has been studied, and a process of directly preparing a planographic printing plate with an inkjet recording ink composition is under study. This is a process where, preferably, on a surface of a hydrophilic support, ink is imagewise discharged by means of an inkjet process, followed by irradiating active radiation thereto to carry out curing, whereby a printing plate having a desired image (preferably, a hydrophobic image) is obtained. In order to form an image portion of a planographic printing plate, it is desired that an ink drop discharged on the support is rapidly cured without causing bleeding, the strength of a cured image portion and the adhesiveness thereof with respect to the support are excellent, and when the planographic printing plate is mounted on a printing machine, the image portion excellently follows the deflection of the support and therefor is not subjected to damage such as cracks. An ink composition suitable for such applications is in demand.
An object of the invention is to provide an ink composition that can be cured with high sensitivity to irradiation of active radiation, form a high quality image, and impart sufficient flexibility to an image obtained after the ink is cured, and an inkjet recording method using the ink composition.
Furthermore, another object of the invention is to provide a planographic printing plate obtained using an ink composition that can be cured with high sensitivity when active radiation (particularly preferably UV rays) is irradiated, and a producing method of the planographic printing plate.